1. Field of the Invention
The present invention is related to the field of heat sinks, and more specifically to a novel arrangement of electric power switches and heat sinks on a printed electric circuit board.
2. Description of the Related Art
Complex electric circuits, such as those of computer units, are often manufactured on generally flat printed circuit boards, which are also known as motherboards. These circuits receive electrical power, and switch it with electrical switches to the various units of the circuit. These switches, also known as power switches, generate heat commensurate with the switched electrical power. It is a common practice to deal with the generated heat by attaching a heat sink to every electrical switch. An example of this is presented below.
Referring to FIG. 1, an electrical switch 50 is now described. The electrical switch 50 includes an electronic component 52, and that is typically encapsulated in electrically insulating material. The electronic component 52 is accessed by three electrical leads 54, 56, 58, which are typically received in holes of the printed circuit board (not shown). The electronic component 52 can be a transistor, an FET, a MOSFET, etc.
When an electrical switch, such as electrical switch 50, is intended for handling large amounts of electrical power, it is often provided with a heat conductive backing. The backing is typically made out of metal, for dissipating the heat generated by the electronic component 52.
Typically, the heat metal backing is provided in the form of tab 62 for the switch 50. In some methodologies, the tab 62 is soldered on the printed circuit board itself.
In a certain methodology, also known as TO-220 methodology, the tab 62 is intended to be arranged upright, perpendicularly to a plane of the printed circuit board, and parallel to the leads 54, 56, 58. The tab 62 includes a hole 64, for passing a screw (not shown). The screw is used to attach a heat sink to the switch 50.
Referring now to FIG. 2, a heat sink 70 is described. The heat sink 70 includes a main panel 72, which includes a hole 74. The hole 74 is for receiving a screw (not shown), for attachment to the switch 50 of FIG. 1. The heat sink 70 also includes two side panels 76, which are also known as fin panels 76. Optionally and preferably, the fin panels 76 include slots 78, which are also known as cuts 78. The heat sink 70 is typically made out of metal, and is painted black for radiating the heat better. In addition, the paint advantageously also provides electrical isolation.
Referring now to FIG. 3, the general attaching arrangement is illustrated. The leads 54, 56, 58 (not shown, but obscured by the electronic component 52) of the device 50 are inserted into holes (not shown, but obscured by the electronic component 52) of the printed circuit board 80. The hole 64 of the tab 62 is aligned with the hole 74 of the main panel 72 of the heat sink 70.
The attaching arrangement also illustrates the weaknesses of this methodology. More particularly, the arrangement of FIG. 3 occupies a lot of space on the printed circuit board 80. In particular, while the switch 50 can be physically small, the heat sink 70 demands a lot of space. This forces locating other devices farther away from switch 50.
The problem is made worse by the fact that typically many electrical power switches, such as switch 50, are designed to be grouped together nearby, for sharing between them the electrical load. Each of them requires a heat sink, and therefore each requires a lot of space around it. Accordingly, the bank of electrical switches occupies a large area of the motherboard.
There's also another reason on why that area cannot be made smaller. Devices having heat sinks are often cooled by use of fan, which establishes an airflow. But it has proven harder to establish an air flow when the heat sinks and the switches are crowded close to each other.
These problems have been addressed in the past by keeping the switches close to each other, and directing their fins away from the group. Another way has been by making each of the heat sinks smaller. This means making the side panels 76 less wide. This also means making the main panel 72 less wide, which brings this side panels 76 closer to the device 50.
But the rating of the heat sink 70 is determined by its dimensions. As the dimensions are getting smaller, to accommodate overcrowding on the board 80, the heat sink 70 can dissipate less heat. This is exactly contrary to the present needs of the industry. As electrical devices increase in capability, they consume more power, which in turn requires higher heat sinking capability. In addition, making the circuit boards larger runs the risk of exceeding standard sizes and form factors, which can adversely affect the acceptance and success of the product in the market.